If each of the a,b,c,d is a decimal digit - for how many ordered quadruplets (a,b,c,d) is the sum S= a+b+6c+d divisible by 3 ?

Answer: within 20 sec.

(In reply to How many are divisible by 1? by Steve Herman)

My understanding of "ordered quadruplets" is that (1,1,1,2) differs from (1,2,1,1), etc., and each counts as a separate ordered quadruplet.

Posted by Charlie on 2014-04-09 12:46:01